One configuration of a conventional layered organic photoreceptor includes in the following order: a substrate, a blocking layer, an optional adhesive layer, a charge generating layer, and a charge transport layer. Of all the layers in a typical photoreceptor, the most poorly understood may be the blocking layer (also referred to in some situations as an undercoat layer). The blocking layer must effectively block hole injection or else poor charge acceptance and high dark decay will result However, the blocking layer must allow the passage of electrons or else high charge buildup at the blocking layer will occur after light discharge. High charge/electric field buildup results in printout defect (dark spots) in the background areas under Discharge Area Development (DAD) scheme. Conventional materials for the blocking layer include gamma-aminopropyltriethoxysilane, phenolic binder-titanium dioxide, polyvinylchloride-polyacrylonitrile emulsion, zirconium/siliane/partly hydrolyzed polyvinyl butyral, and nylon-terpolymer.
A gamma-aminopropyltriethoxysilane blocking layer has certain disadvantages: a thin layer may be difficult to coat uniformly which can cause print defects in areas unwetted by the barrier film, a thin layer also is susceptible to dielectric breakdown in bias charging roll development systems; uncured gamma-aminopropyltriethoxysilane can interact with the charge generating layer which could reduce photoreceptor sensitivity; low viscosity gamma-aminopropyltriethoxysilane solutions generally cannot be used to make thick coatings, but higher solids coating solutions suffer from shelf life stability issues; and because of its high crosslink density, a gamma-aminopropyltriethoxysilane blocking layer is susceptible to cracking. Thus, there is a need, which the present invention addresses, for new blocking layers that minimize or avoid the problems described above for a gamma-aminopropyltriethoxysilane blocking layer.
Conventional imaging members are disclosed in U.S. Pat. Nos. 5,266,431; 5,338,587; and 5,654,118.